It helps okay. I recently used it to slowly and mostly automatically introduce more and more C++11 across a bigger code base. For example it does a great job introducing nullptr [0] and an okay job turning classic for loops into range based for loops [1] where possible.
[0] https://github.com/swift/swift/commit/eddd92ed76ae68cb1e2026... [1] https://github.com/swift/swift/commit/3c560e31b0f168da917e8d...